1. Technical Field
This invention relates generally to a gas concentration sensor, and more particularly to a resealable device for measuring the concentration of a gas in an environment.
2. Discussion
Various industrial operations must be conducted in a specific gaseous environment. For example, some United States military specifications require that products be sealed in an environment other than air, which includes an indicator gas, such as helium or argon. One purpose for this requirement is to facilitate testing to determine whether the products are sufficiently sealed to prevent entry or escape of a gas, or even moisture.
Apparatus for conducting these operations is shown in FIG. 1 and consists of a sealed environment chamber 10 containing a gaseous environment 12 and having a pair of operator's gloves 14, 16 for manipulating objects and tools inside environment 12 by an operator outside of chamber 10. Chamber 10 is coupled to an environment regulation system having an inlet tube 18 and an outlet tube 20 for regulating the composition of, particularly the concentration of a gas in, the gaseous environment 12. Gaseous environment 12 consists generally of inert gaseous components with one type of gas, such as helium, in a specific concentration. Chamber 10 is further provided with a lock chamber 22 containing a lock environment 23 and having an inner and outer door 24, 26 and being equipped with a lock regulation system having an inlet tube 28 and an outlet tube 30 for regulating the composition of the gaseous lock environment, including the lock concentration of a gas, contained within lock chamber 22.
Objects may be placed within environment 12 without substantially altering the composition of environment 12 by opening outer door 26, inserting the object within lock chamber 22, closing outer door 26, using lock regulation system to make lock environment 23 within lock chamber 22 substantially similar to environment 12 within environment chamber 10, opening inner door 24, and placing the object within environment 12. Environment 12 is thereby maintained having a substantially constant gaseous composition while the object is transferred to environment chamber 10. Objects may be removed from environment 12 by reversing the process.
Devices for measuring a gas concentration in an environment chamber generally involve capturing a sample of the environment within a sealed sample chamber. The sample chamber requires a seal which is capable of maintaining an ultra-high vacuum to accurately measure the gas concentration. As a result, prior sensing devices generally were permanently sealed, such as by pinching off a malleable access tube or by welding. These devices may be used only once and are capable of taking only one measurement.
It is therefore desirable to measure the concentration of a gas in an environment with a sensing device which is not permanently sealed and which can make repeated measurements, as well as measure concentrations in multiple environment chambers.